1. Field of the Invention
The present invention relates to a slit lamp microscope for use in a field of ophthalmology, and more specifically to a slit lamp microscope with a special contrivance in its portion related to the formation of a slit.
2. Description of the Related Art
A slit lamp microscope has been used as a kind of microscope for use in the field of ophthalmology. A slit lamp microscope, which makes it possible to observe various lesion parts of an eye to be examined through a contrivance in illumination, is used for day-to-day diagnosis by eye doctors.
JP2003-299619 A (claims, paragraphs [0019] to [0026] in the specification, and FIGS. 1 and 2) discloses an example of the construction of a conventional slit lamp microscope. The slit lamp microscope as disclosed in the above-mentioned publication includes: an illumination system which applies slit light to the eye to be examined (hereinafter simply referred to as “the eye”) through a prism to make it possible to observe a sectional image of the portion of the eye to be observed; a background illumination system which illuminates the periphery of an illumination field of the eye given by the illumination system to make it possible to observe the portion of the eye to be observed and the periphery thereof; an observation system for observing the portion of the eye to be observed and the periphery thereof; a stationary guide member detachably arranged in the vicinity of the prism of the illumination system; and an irradiation unit which holds a light guide member guiding background illumination light from a light source provided in the illumination system, which is arranged so as to draw a turn track with respect to the stationary guide member around the reflection point of the prism or a point in the vicinity thereof, and which applies background illumination light emitted from the light guide member to the prism from a different direction to change the irradiation field with respect to the eye, whereby it is possible to clearly observe not only the lesion part of the eye but, at the same time, the entire image thereof.
In the following, the construction of the conventional slit lamp microscope as disclosed in JP 2003-299619 A will be described with reference to FIGS. 8 through 11. FIG. 8 is a schematic side view showing the external construction of the slit lamp microscope. FIG. 9 is a schematic side view showing the optical configuration of the slit lamp microscope. FIGS. 10 and 11 are a perspective view and a plan view schematically showing how a slit is formed in the slit lamp microscope.
As shown in FIG. 8, the slit lamp microscope 1 includes a base 4 supported on a table 2 so as to be capable of being moved in a lateral horizontal direction and a longitudinal horizontal direction by means of a movement mechanism portion 3, an operating handle (joy stick) 5 adapted to displace the base 4 in the lateral horizontal direction and the longitudinal horizontal direction through tilting operation, an observation system 6 and an illumination system 8 supported by the base 4, and a-chin-rest stand 10 equipped with a chin rest 10a and a forehead pad 10b for the subject arranged opposite to a lens barrel main body 9 accommodating the observation system 6. Provided on a side surface of the lens barrel main body 9 is an observation power adjusting knob 11 for varying the observation power. Further, an imaging device 20, such as a CCD, is connected to the lens barrel main body 9. Further, below the observation system 6, there is arranged a prism 12 for reflecting observation light in the direction of the eye (not shown).
As shown in FIG. 9, the observation system 6 of the slit lamp microscope 1 includes the prism 12, an objective lens 31, a scaling optical system 32, a condensing lens 33, a beam splitter 34, a relay lens 35, a prism 36 for shifting the optical path to the eyepiece lens barrel 9a side, and an eyepiece 37 arranged in the eyepiece lens barrel 9a. An image of the eye E of the subject is formed at an image formation point P, and is observed by an eye Eo of the examiner.
The imaging device 20 includes a condensing lens 41 for condensing the light branched off by the beam splitter 34, a mirror 42 reflecting the light from the condensing lens 41 at right angles, and an imaging camera 43 consisting of a CCD or the like.
The illumination optical system 21 constituting the illumination system 8 includes a light source 51 consisting of a halogen lamp or the like, condensing lenses 52 and 53 for condensing light emitted from the light source 51, a slit 54 allowing transmission of only a portion of the light transmitted through the condensing lenses 52 and 53 to form slit light, a condensing lens 55 condensing the light transmitted through the slit 54, and a strobe light source 56 consisting of a xenon lamp or the like arranged between the light source 51 and the condensing lens 52.
The slit 54 and the eye E are arranged at positions optically conjugate with respect to the condensing lens 55. As a result, slit light (local illumination light) is applied, for example, to the cornea of the eye E, making it possible to observe a sectional image of the cornea.
A background illumination system 70 includes a light guide 71 consisting of an optical fiber serving as a light guide member led out from a position in the vicinity of the light source 51, and an irradiation unit 74 which holds the light guide 71 and which is provided so as to draw a turn track around a reflection point R of the guided light at the prism 12. Part of the light from the light source 51 is guided to the irradiation unit 74 by the light guide 71. The irradiation unit 74 projects the guided light onto the prism 12 from a direction different from that of the light from the illumination system 8 to irradiate the eye E with the light. As a result, the periphery of the lesion part of the eye E is irradiated with the light. The irradiation unit 74 is capable of changing the irradiation field with respect to the eye E.
The slit 54 of the illumination system 8 is formed by a slit forming means 100′ as shown in FIG. 10. The slit forming means 100′ includes left and right casings 100L and 100R. FIG. 11 is a top view of the casings 100L and 100R. When it is said right or left, it means here the direction as seen from the examiner, that is, the direction as seen from the eyepiece lens barrel 9a shown in FIG. 8.
The casings 100L and 100R are arranged so as to form a cylinder with a gap 109 therebetween. Further, the casings 100L and 100R respectively have pairs of protrusions 100L′ and 100R′ arranged at positions opposed to each other. The protrusions 100L′ and 100R′ are configured so as to constitute a part of the cylinder. Further, as shown in FIG. 11, formed in the bottom surfaces of the casings 100L and 100R are screw holes 108L and 108R for providing through threaded engagement a pair of slit blades forming the slit 54 (see slit blades 107L and 107R in FIG. 3 described below).
Protruding from the outer peripheral surfaces of the casings 100L and 100R of the slit forming means 100′ are bearings 101L and 101 R so as to be spaced apart from each other by a predetermined distance. The bearings 101L and 101R are provided only on the front side as seen in FIG. 10. The protrusions 100L′ of the casing 100L and the protrusions 100R′ of the casing 100R are fitted into ring members 105 while holding columnar shaft members 102 therebetween. As a result, the casings 100L and 100R are connected so as to be rotatable around the shaft members 102. The shaft members 102 and the ring members 105 are provided respectively for the pairs of protrusions 100L′ and 100R′ arranged in an opposed relation.
When the examiner performs a predetermined operation to change the width of the slit 54, an ascent/descent shaft 86 is moved in the axial direction thereof, that is, vertically. A Mount-Fuji-shaped inter-casing distance varying member 87 with tapered sides is fixed to the upper end of the ascent/descent shaft 86 by screws 87a. The tapered sides of the inter-casing distance varying member 87 are arranged so as to be held in contact with the bearings 101L and 101R.
In order to reliably hold the side surfaces of the inter-casing distance varying member 87 in contact with the bearings 101L and 101R and to avoid slippage or the like as much as possible, the casings 100L and 100R are equipped with an urging means (not shown) consisting of a spring or the like urging the casings 100L and 100R so as to bring the above-mentioned pair of slit blades close to each other. The urging means also exerts urging force so as to press the protrusions 100L′ and 100R′ of the casings 100L and 100R against the shaft members 102. As the urging means, there is provided, for example, a U-shaped spring on the inner peripheral surfaces of the casings 100L and 100R. The U-shaped spring is arranged at a position lower than the shaft members 102 constituting the rotation shafts of the casings 100L and 100R, that is, at a position nearer to the slit blades than the shaft members 102.
The inter-casing distance varying member 87 moves vertically with the ascent/descent shaft 86. When it moves upwards, the. inter-casing distance varying member 87 functions so as to increase the distance between the bearings 101L and 101R. As a result, the casings 100L and 100R are rotated around the shaft members 102 so as to enlarge the gap 109. With this rotation, the distance between the pair of slit blades mounted to the bottom surfaces of the casings 100L and 100R increases, and the width of the slit 54 increases. When, in contrast, the inter-casing distance varying member 87 moves downwards, the distance between the bearings 101L and 101R is reduced, and the casings 100L and 100R are rotated around the shaft members 102 so as to diminish the gap 109, reducing the distance between the pair of slit blades to diminish the width of the slit 54.
It should be noted that the slope of the sides of the inter-casing distance varying member 87 is formed so as to be relatively steep in the upper portions and relatively gentle in the lower portions thereof. Thus, when the width of the slit 54 is small, fine width adjustment is possible, and, when the width of the slit 54 is to be increased, it can be done so at a stretch.
The conventional slit lamp microscope, constructed as described above, is known to have a number of problems.
First, since the slope of the lower portions of the side surfaces of the inter-casing distance varying member 87 is gentle, slippage is likely to occur between the side surfaces and the bearings 101L and 101R, and, due to the urging force of the urging means, it can happen that slippage actually occurs to cause the slit 54 to close spontaneously. This leads to a deterioration in the accuracy in the slit width, which is of importance in observation by using the slit lamp microscope. Further, when such spontaneous closing occurs, additional time is required to re-adjust the slit width, resulting in an increase in inspection time, which leads to an increase in the physical burden on both the examiner and subject. In particular, for the examiner, who has to examine a number of patients a day, such spontaneous closing of the slit is nothing but a bother.
When the urging force is weakened in order to avoid slippage between the side surfaces of the inter-casing distance varying member 87 and the bearings 101L and 101R, the connection between the casings 100L and 100R and the shaft members 102 is loosened, so that there is a fear of a problem arising in terms of the parallelism of the slit as described below.
To prevent spontaneous closing of the slit, there is often provided a brake means for braking the descent of the ascent/descent shaft 86 and the inter-casing distance varying member-87. Usually, this brake means is accommodated in a knob for performing the operation of opening or closing the slit, and consists of something like a disk brake for restraining rotation of the knob. In a typical case, a felt member is used as the disc, and braking is effected by compressing the felt member by means of a spring or the like through the intermediation of a washer or the like. Apart from this, a brake means is used which restrains knob rotation through adoption of a wave washer.
In such conventional brake means, which is adapted to restrain knob rotation as described above, the rotation of the knob is rather heavy. Accordingly, a great force is needed when adjusting the slit, which is disadvantageous in terms of operability.
It might be possible to effect design change so as to make the slope of the side surfaces of the inter-casing distance varying member 87 steeper; it should be noted, however, that the conventional slope configuration has been adopted for such a long time that many examiners are quite used to the relationship between its operating amount and slit width change; thus, such design change is not so desirable from the viewpoint of operability.
Another problem in the prior art is related to the parallelism of the slit. When observing and inspecting an eye by using a slit lamp microscope, it is desirable for the slit to be formed parallel. In the prior-art technique, however, there are cases in which it is rather difficult to form the slit parallel. It is to be assumed that the difficulty is due partly to the heat of the light source and partly to the accuracy at the time of production.
When a slit lamp microscope is used for a long period of time, the interior of the apparatus may attain high temperature due to the heat from the light source. The temperature attained can be as high as approximately 60° C. In view of this, the ring members 105 are formed in a somewhat large size taking into account the thermal expansion of the protrusions 100L′ and 100R′ of the casings 100L and 100R, of the shaft members 102, and, further, of themselves. Accordingly, depending upon the temperature inside the apparatus, the connection between the protrusions 100L′ and 100R′, the shaft members 102, and the ring members 105 can be loosened. That will make it impossible for the casings 100L and 100R to rotate uniformly to the right and left, resulting in formation of a distorted slit which is not parallel.
Similarly, the parallelism of the slit can be influenced by production errors in the casings 100L and 100R, the shaft members 102, and the ring members 105.